/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.io;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtIncompatible;

import java.io.IOException;
import java.io.InputStream;
import java.util.Iterator;
import javax.annotation.CheckForNull;

/**
 * An {@link InputStream} that concatenates multiple substreams. At most one stream will be open at
 * a time.
 *
 * @author Chris Nokleberg
 * @since 1.0
 */
@GwtIncompatible
@ElementTypesAreNonnullByDefault
final class MultiInputStream extends InputStream
{

    private Iterator<? extends ByteSource> it;
    @CheckForNull
    private InputStream in;

    /**
     * Creates a new instance.
     *
     * @param it an iterator of I/O suppliers that will provide each substream
     */
    public MultiInputStream(Iterator<? extends ByteSource> it) throws IOException
    {
        this.it = checkNotNull(it);
        advance();
    }

    @Override
    public void close() throws IOException
    {
        if (in != null)
        {
            try
            {
                in.close();
            }
            finally
            {
                in = null;
            }
        }
    }

    /**
     * Closes the current input stream and opens the next one, if any.
     */
    private void advance() throws IOException
    {
        close();
        if (it.hasNext())
        {
            in = it.next().openStream();
        }
    }

    @Override
    public int available() throws IOException
    {
        if (in == null)
        {
            return 0;
        }
        return in.available();
    }

    @Override
    public boolean markSupported()
    {
        return false;
    }

    @Override
    public int read() throws IOException
    {
        while (in != null)
        {
            int result = in.read();
            if (result != -1)
            {
                return result;
            }
            advance();
        }
        return -1;
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException
    {
        checkNotNull(b);
        while (in != null)
        {
            int result = in.read(b, off, len);
            if (result != -1)
            {
                return result;
            }
            advance();
        }
        return -1;
    }

    @Override
    public long skip(long n) throws IOException
    {
        if (in == null || n <= 0)
        {
            return 0;
        }
        long result = in.skip(n);
        if (result != 0)
        {
            return result;
        }
        if (read() == -1)
        {
            return 0;
        }
        return 1 + in.skip(n - 1);
    }
}
